None.
None.
The present invention relates to ultrasound systems which image anatomical structures and the movement thereof. More particularly, the present invention relates to a method and apparatus for displaying in real-time a slow motion ultrasound image.
Recent advances in ultrasound technology have made it possible to acquire ultrasound images with frame-rates that exceed the limitations given by the human eye and current video standards such as PAL and NTSC. The human eye recognizes about 30-50 frames per second, but 100-300 images can be acquired each second with current high performance ultrasound systems.
The increase in frame-rate offers significant new clinical information because physiological events in, for example, cardiology can be extremely rapid and cannot be resolved with frame-rates less than 30 frames per second. An example of a physiological event that requires a high frame-rate to resolve is cardiac valve motion. At 30 frames per second, only a few image frames are available to study the opening of a valve. At 300 frames per second, one can study details in the motion pattern of the valve during the opening. Similarly, myocardial motion and contraction cannot be satisfactorily resolved at 30 frames per second. Tissue velocity imaging and strain rate imaging are difficult to grasp in real-time due to the rapid changes in color display. New techniques recently developed for blood motion imaging are capable of producing a 2D motion pattern of blood flow at for example 200 frames per second, well above the maximum perception rate of the human eye. These new techniques will therefore benefit from slow motion.
It is a limitation of current ultrasound systems that the additional information provided by high frame-rates cannot be satisfactorily visualized by the human eye or recorded on video during live scanning. A current procedure for visualizing high frame-rate ultrasound includes the steps of: acquiring and digitally storing ultrasound information, stopping the acquisition and replaying a stored period of ultrasound information in slow motion. The length of the stored period may coincide with a physical event, such as a heartbeat. A video recorder may be used to record the slow motion playback.
A further problem confronting the field is the live display of ultrasound diagnostic modalities that are too computationally intensive to allow the display to keep up with the acquisition rate. With current technologies, such a situation must be handled by either lowering the acquisition frame-rate, skipping frames in the display, or limiting viewing to a replay of data that is processed off-line in less than real-time.
A still further problem confronting the field is the need to acquire additional ultrasound information without changing the display during live scanning. For example, during stress echo analysis, it is desirable to have a continuous live display of high quality 2D images during scanning, but at the same time acquire additional information like tissue velocity imaging and strain rate imaging. It is also desirable to afford continuous live display while retrieving and accessing tissue velocity imaging and strain rate imaging to quantify wall motion and wall thickening.
U.S. Pat. No. 4,572,202 to Thomenious et al. describes a way to alternate between periodically acquiring ultrasound information at a rate which is greater than the perception rate of the human eye, recording the acquired information over a short period of time and displaying, in an off-line mode (as opposed to a live display), the recorded information at a lower rate than the acquisition rate. The period over which ultrasound information is acquired and recorded is triggered, for example, based on the trace produced on an electrocardiogram so that part of the cardiac cycle can be studied. The playback rate during display may be manually or automatically adjusted. While providing clinically useful information, the system described in the Thomenious patent has a number of limitations, such as difficulty in displaying complete heart cycles. Also, in the system of the Thomenious patent, ultrasound information is only recorded periodically during short time intervals, relatively long time lags exist between acquisition and display, variations in heart rate from beat to beat may cause xe2x80x9cflickerxe2x80x9d in the display, and ultrasound information is not acquired, recorded or displayed during the time between recording periods.
A need remains for an improved ultrasound system to overcome the above-identified difficulties and limitations.
A system and method are provided for acquiring ultrasound information at an acquisition rate and displaying at least a portion of the acquired ultrasound information at a display rate that is slower than the acquisition rate. Ultrasound information may be continuously acquired and stored at a frame-rate that is greater than the perception rate of the human eye. At least a portion of the acquired ultrasound information is displayed at a frame-rate that allows human perception. Acquisition and display are synchronized from time-to-time upon satisfaction of a synchronization condition. The synchronization condition may be related to a predetermined time interval or a triggering event generated by or through triggering generated by, for example, a physiological event detected in, for example, an ECG trace. Acquired ultrasound information is, thus, displayed in a real-time slow motion manner that maintains real-time synchrony and yet provides a display rate that is lower than the acquisition rate and preferably lower than the maximum perception rate of the human eye.
The real-time slow motion display of ultrasound information may be displayed alone or simultaneously with a display of the ultrasound information having a display rate equal to the acquisition rate. A real-time slow motion display may also be combined with a triggered M-mode display that allows a user to manually select triggering events or time intervals.
According to another aspect of a preferred embodiment of the present invention, the acquisition of ultrasound information may be performed according to a first acquisition mode during a first acquisition period and a second different mode during a second acquisition period. The ultrasound information acquired during the first acquisition period may be displayed at a display rate that is slower than the acquisition rate such that a portion of the ultrasound information acquired during the first acquisition period is displayed during the first acquisition period and a portion of the ultrasound information acquired during the first acquisition period is displayed during a second acquisition period. The ultrasound information acquired during the first acquisition period may be displayed separately or stored for off-line display.
According to another aspect of a preferred embodiment of the present invention, ultrasound information is acquired at an acquisition rate and processed at a processing rate that is lower than the acquisition rate and displayed at a display rate than is the same as or lower than the processing rate while acquisition of ultrasound information is ongoing. Acquisition and processing are synchronized from time-to-time in the manner described above.
Other objects, features, and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below.